The present invention relates to a system for correlating a series of signals fed sequentially from a number of sensors with the printout of the signals on a remote recorder and more particularly to a method and means for monitoring the operation of rotary kilns for example, of the type used for directly reducing metal oxides with solid carbonaceous materials as the source of fuel and reductant, by sensing the internal kiln conditions, such as temperatures, and displaying the sensed results at a remote location on a multipoint recorder wherein the signals are properly sequenced to correlate the sensing position on the kiln with the sensed signal on the recorder.
Temperature sensing and control is essential to the proper operation of a rotary kiln carrying out a direct reduction process such as the reduction of iron ores to directly reduced iron (DRI) or sponge iron using coal as the fuel and reductant. The temperatures within the kiln must be regularly sensed and accurately displayed to permit the kiln operators to supervise the process and initiate any necessary process changes or corrections promptly. The temperature sensors for this purpose have typically been thermocouples which are disposed at spaced locations along the length of the kiln and which transmit low level millivolt signal data from each location on the rotating kiln to a recorder in a central control room. The common technique has been to transmit the signals over fixed wires routed from each of the thermocouples along the kiln shell to a set of slip rings at a convenient central location on the kiln. The signals are then transferred from the slip rings, through a set of sliding shoes at a stationary location adjacent the kiln, and routed over further wires to the control room recorder. An example of a prior art system of this type is shown in U.S. Pat. No. 3,331,247 to Toepell wherein temperature indicative millivolt signals are generated from a number of thermocouples on a kiln, each of which thermocouples has one terminal connected to a common continuous slip ring mounted on the kiln and another terminal connected to a separate segment of a segmented slip ring. A mechanically-actuated recorder switching system is also mounted on the kiln to permit transfer of the thermocouple signal voltages to an external receiver in a sequential sampling sequence through brushes contacting the two slip rings. The switching system must activate a print mechanism on the receiving recorder to ensure correct sequencing and correlation between the recorded signal and the proper thermocouple location. Other mechanical and/or magnetic proximity switching activated by tabs or levers on the kiln have been used in this application, but these prior art systems have been plagued with a number of problems. Since such kilns expand as they are heated and contract when rained upon, and move forward and backward in normal operation, the movement between tabs on the kiln and pickups fixed adjacent the kiln results in broken switch arms, destroyed switches, the need for spacing adjustments, and other heavy maintenance requirements. Even with frequent calibrations and thorough understanding of the system, accurate interpretation of the data is difficult, and as calibration verification is normally accomplished with the kiln stopped, errors due to the sliding action between the rings and the stationary shoes during kiln operation are not taken into consideration.
The present invention is directed to providing a system which eliminates many of the problems inherent in such prior art temperature-measuring systems and which is particularly suitable for use with a thermocouple system such as disclosed in copending U.S. application, Ser. No. 250,006, assigned to the same assignee as the present application.